Long wavelength tunable single-longitudinal-mode lasers have been developed for over a decade mainly for telecommunication applications. Various types of 1.5 μm tunable lasers have been used including distributed Bragg reflector (DBR) lasers, optically or electrically pumped vertical cavity surface emitting lasers (VCSELs) integrated with micro-electro-mechanical system (MEMS), distributed feedback (DFB) laser arrays, and others. Especially, multi-section DBR lasers employing non-uniform grating structures such as super-structure gratings or sampled gratings have shown a wide tuning range by carrier injection. However, the fabrication process steps involved are demanding, and sophisticated control electronics are often required to adjust the currents to different sections, such as, active section, passive DBR section, and phase control section, in order to obtain a wide tuning range and avoid mode hops while maintaining a constant output power.
Even though DFB lasers have shown a narrower tuning range compared to DBR lasers, DFB lasers advantages include a much simpler fabrication process and no need for sophisticated control electronics. Additionally, DFB laser technology is the only technology that is currently mature. Thermal tuning is usually employed for DFB lasers because only a very small tuning is possible by carrier injection due to two adversely competing processes, that is, the thermal effect and plasma effect. There are at least two different techniques to tune DFB lasers thermally using an external thermo-electric cooler (TEC, or Peltier cooler) and using an integrated thin film heater. The first approach requires a lot of power and the tuning speed is very slow because the cooler needs to heat and cool the laser as well as the submount and heat sink. There have been several reports on 1.5 μm InGaAsP/InP DFB and DBR lasers integrated with thin film heaters, but the heater current required to obtain a tuning range of 3.0 nm was 200 mA, which is more than a factor of four higher than the laser operating current to obtain an output power of 5 mW. This high heater current has been an obstacle for these lasers to find practical applications and is due to the low electrical resistance from Pt thin films formed by evaporation processes. Platinum is a metal having inherently low electrical resistance and generally not suitable for use as a heating element. Platinum has been deposited using semiconductor fabrications processes such as evaporation, sputtering, and focused ion beam (FIB). However, FIB deposited platinum is generally not suitable for use in microelectronic devices because of the carbon contamination associated with platinum deposition processes. When depositing platinum using FIB technique, the film shows high electrical resistance and much effort has been devoted to remove contaminating carbon without result. These and other disadvantages of FIB deposited platinum films can be used for the benefit of improving tunable lasers using the invention.